Image intensifier tube



Aug. 5, 1952 J. w. COLTMAN ET AL IMAGE INTENSIFIER TUBE Filed March 11, 1950 Fig.l.

Cesiuted Antimony Zinc sulphide Composite Loyer INVENTORS John W. Colfmopa Richard L. Longlm.

WIYNESSES: A?

ATTORNE Patented Aug. 5, 1952 burgh, Pa.,- assignors to Westinghouse Electric" Corporation, EastPittsb cf Pennsylvania urgh, Pal, a corporation 1 Application March 11, issogserial No. 149,121

' 161Claims.

1 Our invention relates to structures for'image intensifiers of the general type shown in Longini and Hunter copending application Serial No. 771,112, filed August 28, 19 17, which is now U. S. Patent No. 2,555,545, granted June 5, 1951, and assigned to the Westinghouse Electric Corporation of East Pittsburgh, Pennsylvania. Certain subject matter herein disclosed is described and claimed in that application. 7

Such image intensifiers are provided-at one 'endwith a fluorescent screen in-close'contiguity to a photoelectricallf. emissivesurface, and at the other end with a'phosphor screen adapted to emit light when electrons impinge upon it. In such arrangements alight imag is excited on the fluorescent screen, which in turn generates an electron image on" the contiguousphotoelectric surface. The electron'siormingthe lastmentioned image are accelerated. to high velocities and focused by anelectron lens' 'system on a phosphor screen'on the other endfof the tube producing there a, light image, preferably of smaller dimensions but much-higher intensity, than the light image on the fluorescentgscreen. The high intensity light image on the phosphor screen is viewed through a"suitable lens system to obtain an intensified'replicw'of' thei'image excited on the fluorescent screen. An image inten sifier tube of the type 'just' describedi's'i1lustrated in Fig. l of this applicationfl The manufacture of image intensifiers of the type justdescribed presents 'many diflicult problems, and the inven tions which we hereindescribe are efiective solutions of some of these. For example, it is desirable to utilize the most effi cient"'phcsphcrphoto-electric "surface combination'at the input end of the intensifier. This combination'may be a" silver activated zinc sulphide phosphor. and a cesium antimony photoelectric surface as described in Patent 2,523,132 of Coltman and Mason and in a cop-ending application Serial No. 1'09 58- for l?hoto-Sensitiv Apparatus both filed on or about August 10, 1949, which claimcertain submetals; which areordinarily thoughto f'as the 2 to deposit on the antimony surface. However, we have found that the zinc cadmium sulphide phosphor screen is highly sensitive to attack by the cesium vapors which are necessarily generated-during the above-described process.

Another problem which arises in the produc' tion of such image intensifier tubesoriginates in the fact'that the material used to'constitut'e the photoelectrically emissive screenhasanextremeiy high electrical resistance. Where input screens of, considerable size are'to be employed,

the electric current, which must 'flow through the screenwhenelectrons are emitted from various points'on its surface, causes a potential drop separating the'fluorescent material from the photoelectric-material at the input screen shall be highly transparent to the light emittediby the fluorescent particles. Hence, thin layers of most only available electrical conductors, cannot ordinarily be employed to reduce the resistance of the input'screen. Certain metals, such as mag nesium and tun'g'stenycan be used in very thin layers which are not homogeneous, but their transparency is not very high. It has been found that thinlayers of gold or silver, Which'are trans parent toblue light andar'e conducting doIlOt constitute a suitable base for a cesium antimony photoelectric'surface. g

An; extremely important advantage of conductivity in the screen at which'the electronimage originates is that it'preventswarping-of the electric held in the electron lens used to focus the electron image; where suchwarping'is present efiective focussing' is vitiated. One object of our invention is to provide acouducting layer separating the fluorescent material.

from the photoelectric material at the "input screen which shall be at once sufficientlyconductive electrically; transparent to light,- and'be a suitablebasefor cesium antimonyphotosurfaces. k I

Another object of our'invention is .to provide suflicient conductivity along the surface adjacent the photoelectric; material in which an electron image originatesis that it. prevents warping of field of an electronic focussing system acting thereon. I 7

Other objects of my inventionwillbecome a'pparent upon reading the following description, taken in connection with the drawing, in which Figure 1 is a cross-sectional view forming a schematic type showing an image intensifier embodying the principles of my invention; and

Fig. 2 is a.detailed cross-sectional View of a screen forming a part of Fig. 1.

Referring in detail to Fig. 1, the image intensifler comprises a glass envelope I subdivided into three sections which are joined vacuum tight to each other by two gasket seals 2 and 3.- The gasket seals 2 and 3 each comprises a pair of annular metallic memberswith a gasket of gold interposed between them against which theyare tightly clamped by suitable bolts or other means (not shown). The metal rings are Welded to rings 4, 5 and 6 of the alloy Kovar which are sealed to the glass portions of the envelope in accordance with the application Serial No. 80,377, of R. O. McIntosh, filed March 9, 1949, and assigned to the Westinghouse Electric Corporation.

At the smaller end of the container l is positioned the outputscreen 1 which comprises a glass window coated on its interior surface with the phosphor zinc-cadmium sulphide, which latter is backed in turn with a thin layer of aluminum. At the opposite end of the envelope 8 is positioned the input screen 8 which comprises a thin sheet of aluminum which may, as shown, be slightly concave and which has on its inner face a layer 8A of a fluorescent material such as zinc sulphide. Such input screens are described inmore detail in copending application Serial No. 101,964 of W. J. Hushley, filed June 29, 1949, for Method of Making Screens of a Phosphor Embedded in Glass, and assigned to the Westinghouse Electric Corporation.

Fig. 2 shows a cross sectional view to larger scale of screen 8. g In accordance with one feature of our present invention, the surface of the composite fluorescent layer is covered with a thin layer 83 of tin oxide of a particular type. We have found that this form of tin oxide layer can be produced by applying tin chloride, fluoride, or-other tin salts with volatile negative radicals such as the nitrate or sulphate to the heated screen. For best results a tin halide is combined with an organic material and particles hydrolized with water and acid. An example which has been found to be suitable consists of a saturated solution of Si'iClz ZHzO in acetone with 3 cc. Hzo and 5 cc. HCl concentrated solution per 100 cc. solution. The glass coated fluorescent screen produced. for example, as disclosed by W. J. Hushle in his above-mentioned application is heated to a temperature of substantially 640 0., and the abovementioned solution is then sprayed onto it. The electrical conductivity of the layer 8B depends upon the temperature of the screen, and is a maximum for one temperature. We have found that the coating is most suitable as a photoelectricv base when the spraying is done at a temperature much higher than that which would produce such optimum conductivity however.

,We have likewise found that there are many organic compounds of tin which may be employed instead of the tin chloride above mentioned. For example, dibutyltin dichloride has been found suitable for employment. The mode of application of these tin components to the screen are substantially the same as those just described above.

Such materials have been found to readily produce a resistivity of 100,000 ohms per square 4 or less. We have found such resistivities to be eminentl satisfactory for image intensifier purposes.

Another type of conducting layer may be produced by directing onto the heated screen of the above-mentioned Hushley application the vapor ofsilicon tetrachloride. Such a vapor stream may for example be produced by passing air through a chamber containing that substance. For best results the sprayed surface should then be reheated in a muiiie furnace or the like in an atmosphere of illuminating gas and cooled in said atmosphere.

The fluorescent screen produced and coated with conducting layer as above described may be supported in position inside the envelope l by a system of metal support rods 9. The support rods 9 may be attached to the glass envelope by Kovar cups ll sealed to tubulations on the glass envelope.

The envelope I is provided with a number or tubulations I2 through which support rods and inleading wires for the components of the electron lens system may be passed through the walls of the tube The electron lens system comprises I annular metal conductors l3 which are supported on metal rods sealed through the tubulations l2 by Kovar cups such as have already been shown at I l.

The antimony and cesium are deposited on the screen 8 only after the tube structure so far described has been assembled, made vacuum tight, and heat treated in a furnace while evacuating to outgas its parts. One of the tubulations I2 is provided with a metal tube supported on a Kovar seal, and the evacuatin pumping system is connected to this tube. Two others of the tubulations [2 are respectively provided with inlet conduits, through one of which a suitable boat containing antimony may be moved into the axial region of the container I in front ofthe input screen. Through the other tubulation a small capsule from which the cesium vapor may be evolved by heat is likewise pushed into the axial region in front of the input screen.

After the container l is thoroughly exhausted and heat treated to outgas its interior surface, the antimony boat is pushed into position in front of the input screen and heated so that its vapor condenses in a thin layer all over the concave surface of the screen. The container for the antimony is then withdrawn from the tube, and the capsule containing the cesium is advanced to the axial position whence the tube is heated sufllciently so that the antimony surface will react with cesium vapor. It is likewise thereafter withdrawn from the envelope l and the conduits through which the antimony and cesium were introduced and through which the tube is exhausted are sealed off outside the tube.

When the tin oxide type of conducting layer has been applied the antimony surface is preferably maintained at C. or slightly lower durin cesium sensitizing. Higher temperatures may result in deterioration of the tin oxide layer.

We claim as our invention:

1. An image screen comprising a support substantially transparent to X-rays, a first coating comprising a coating of fluorescent material thereon, a second coating comprising tin oxide on said fluorescent coating. and a photoelectrically sensitive coating on the surface of said secon coating.

2. An image screen comprising a support transparent to X-rays, a first'coating comprising a coating of fluorescent material thereon, a second coating comprising silicon oxide on said first coating, and a third coating comprising a photoelectrically emissive substance on said second coating.

3. An image screen comprising a support which is transparent to X-rays, a first layer on said support comprising a substance which emits light where X-rays are incident upon it, a second layer which is transparent to light and which has substantial electrical conductivity covering said first layer, and a third layer comprising a photosensitive substance on said second layer.

4. An image screen comprising a support which is substantially transparent to X-rays, a layer of material on said support which emits light under incidence of X-rays, a second layer consisting of tin oxide on said first layer, and a layer of antimony on said second layer, the surface of said antimony layer being sensitized by cesium.

5. An arrangement for producing an electron image which is a replica of a projected radiation field which comprises a support transparent to the radiation of said field, a first layer comprising a substance which emits light upon incidence of said radiation, a second layer comprising a substance having substantial electrical conductivity and which is substantially transparent to light adjacent said first layer, and adjacent said second layer a third layer which emits electrons under incidence of light.

6. An arrangement for producing an electron image which is a replica of a projected radiation field which comprises a support transparent to the radiation of said field, a first layer of a substance which emits light upon incidence of said radiation, a second layer comprising tin oxide adjacent said first layer, and a surface which emits electrons under incidence of light adjacent said second layer.

7. An image intensifier device comprising an evacuated container having at one end an output screen which emits light in response to incidence thereon of moving electrons and having at the other end an input screen comprising a support member, a first layer of material which emits light upon incidence of an input radiation field, a second layer adjacent to said first layer and comprising a substance which has substantial electrical conductivity and which is substan tially transparent to light, and a third layer comprising a material which emits electrons in response to incidence of light.

8. An image intensifier device comprising an evacuated container having at one end an output screen which emits light in response to in cidence thereon of moving electrons and having at the other end an input screen comprising a support member, a first layer of material which emits light upon incidence of an input radiation field, a second laver adjacent to said first layer and comprising silicon oxide, and a third layer comprising a photoelectrically emissive substance.

9. An image intensifier device comprising an evacuated container having at one end an output screen which emits light in response to incidence thereon of moving electrons and having at the other end an input screen comprising a support member, a first layer of material which emits light upon incidence of an input radiation field, a second layer adiacent to said first layer and comprising tin oxide, and a third layer adiacent said second layer and consisting of a Photoelectrically emissive substance.

10. The method of forming an image screen which comprises forming a layer of fluorescent material with a radiation-transparent support, exposing the surface of said screen while hot to the vapor of a tin salt having a volatile negative radical.

11. The method of forming an image screen which comprises forming a layer of fluorescent material with a radiation-transparent support, exposing the surface of said screen while hot to the vapor of a tin salt having a volatile negative radical, and thereafter applying a photosensitive layer on said surface.

12. The method of forming an image screen which comprises forming a layer of fluorescent material with a radiation-transparent support, exposing the surface of said screen while hot to the vapor of a tin salt having a volatile negative radical, and thereafter applying a photosensitive layer on said surface, the temperature of said hot surface being higher thanthat which produces optimum electrical conductivity in the resulting coating.

13. The method of forming an image screen which comprises forming a layer of fluorescent material with a radiation-transparent support, exposing the surface of said screen while hot to the vapor of a tin salt having a volatile negative radical, thereafter coating said surface with antimony and exposing said antimony coating to cesium vapor.

14. The method of forming an image screen which comprises forming a layer of fluorescent material with a radiation-transparent support, exposing the surface of said screen while hot to the vapor of a tin salt having a volatile negative radical, thereafter coating said surface with antimony and exposing said antimony coating to cesium vapor at a temperature of about degrees centigrade.

15. The method of forming an image screen which comprises forming a layer of fluorescent material with a radiation transparent support,

exposing the surface of said screen while hot to the vapor of a tin salt having a volatile negative radical, the tem erature of said hot surface being higher than that which produces optimum electrical conductivit in the resulting coating, thereafter coating said surface with antimony and exposing said antimony coating to cesium vapor. 16. The method of forming an image screen which comprises forming a laver of fluorescent material with a radiation-transparent support, exposing the surface of said screen while hot to the vapor of a tin salt ha ing a volatile negative radical. the temperature of said hot surface being higher than that which produces o timum electrical conductivity in the resulting coating, thereafter coating said surface ith antimony and exposing said antimony coating to cesium vapor at a temperature of about 140 degrees centigrade.

JOHN W. COLTI AN. RICHARD LQLONGINI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2.523. 32 Mason et al. Sept. 19, 1950 5 6,5744 Mendenhall Oct. 1'7, 1950 

